optical fiber, cable core structure of layer stranded. Once successively in Shanghai, Beijing, Wuhan and other places to carry out field test. Soon after the local telephone network as interoffice trunk trial, after 1984, gradually for the long haul, and began using single-mode fiber. Communication cables with a transmission capacity greater than copper wire, the relay distance long, small volume, light weight, no electromagnetic interference, since the wired transmission line shaft after 1976 has developed into the trunk, the trunk, offshore and transoceanic submarine communication, as well as the local area network, private network and so on, and has begun to develop local user loop distribution network field, provides a transmission line for fiber to the home, the broadband integrated services digital network.
     The optical network is a cornerstone of the information highway
     Fiber optic cable is the main transmission tool in today's information society, various kinds of information network. If the "Internet" known as the "information superhighway", then, - optical network optical network is the cornerstone of information highway is the physical routing internet. Once a cable damage and blocking, the direction of the "information superhighway" will destroy. Through the optical transmission of information, in addition to normal telephone, telegraph, fax, and TV signal transmission, information is not a moment to break the bank remittance, the stock market etc.. Transmission method of long distance communication cable has evolved from PDH to SDH, the transmission rate has been from the original 140MB/S to 2.5GB/S, 4 x 2.5GB/S, 16 x 2.5GB/S or more, that is to say, one of the core can be opened 30000, 120000, 480000 or even more road to development. The transmission capacity of such a large, cable once blocked not only caused huge losses to the telecommunications sector, but also because of poor communication, may cause some inconvenience to the masses, such as computer users can not access, the stock market is not known, bank remittance cannot, remote access into not bubble, all kinds of information transmission. In the outlying mountainous area, once the cable is interrupted, will make the county or several counties in communication optical cable line retire, become islands. Due to the government organs and people's loss is immeasurable.